Understanding Vitamin K2 and Its Forms
Vitamin K is a fat-soluble vitamin found in two main forms: vitamin K1 (phylloquinone) and vitamin K2 (menaquinones). While K1 is primarily found in green leafy vegetables and is essential for blood clotting, K2 plays a far more specialized and vital role in regulating calcium metabolism. This involves activating proteins that help build strong bones and prevent calcium from accumulating in soft tissues, like the arteries.
Vitamin K2 itself is not a single compound but a family of related molecules known as menaquinones (MKs). The most important and well-researched forms are MK-4 and MK-7. MK-4 is primarily found in animal products like organ meats, egg yolks, and dairy fat from grass-fed animals. MK-7, on the other hand, is a longer-chain menaquinone produced by bacterial fermentation and is more efficiently transported to extrahepatic tissues, where it is highly beneficial for bone and heart health.
The Top Source: Natto
Without a doubt, the highest concentration of vitamin K2 is found in natto, a traditional Japanese food made from fermented soybeans. The fermentation process, which uses the bacteria Bacillus subtilis, produces exceptionally high levels of the long-chain menaquinone, MK-7. A 100-gram serving of natto can contain over 1000 mcg of vitamin K2, making it an incredibly potent source. Despite its nutritional prowess, natto has a distinctive, pungent smell and sticky texture that many in Western cultures find unpalatable. This often makes it a difficult food to incorporate into a regular diet for those not accustomed to it.
Other Rich Food Sources of K2
While natto may be in a league of its own, several other foods contain significant amounts of vitamin K2, offering more palatable options for most people.
Animal-Based Sources (Rich in MK-4)
- Goose Liver Pâté: This delicacy is another top contender for K2 content, with a 100-gram serving providing a substantial amount of the MK-4 form.
- Organ Meats: Chicken liver, in particular, is a great source of MK-4. Pan-fried chicken liver can offer a healthy dose of vitamin K2.
- Egg Yolks: The vitamin K2 content in egg yolks, especially from pasture-raised or free-range hens, can be quite high, with some studies citing up to 192 mcg per yolk, depending on the hen's diet.
- Dairy Products (from grass-fed animals): Certain dairy products, particularly those from grass-fed cows, are good sources of MK-4. This includes grass-fed butter and full-fat dairy products.
Fermented and Dairy Sources (Rich in MK-7, MK-8, and MK-9)
- Hard Cheeses: Aged hard cheeses like Gouda and Edam are notable sources of the longer-chain menaquinones (MK-7, MK-8, MK-9). The K2 content tends to increase with the cheese's age.
- Soft Cheeses: Soft fermented cheeses such as Brie and Camembert also provide a good amount of vitamin K2.
- Sauerkraut: While not as rich as natto, this fermented cabbage dish contains smaller but still beneficial amounts of MK-7.
A Comparison of Vitamin K2 Food Sources
| Food Source | Primary MK Form | Average K2 Content (per 100g) | Notes |
|---|---|---|---|
| Natto | MK-7 | Up to 1000 mcg | Highest known source; has a strong flavor and texture. |
| Goose Liver Pâté | MK-4 | ~369 mcg | A very rich animal source. |
| Hard Cheeses (e.g., Gouda) | MK-8, MK-9 | ~76 mcg | Content varies; increases with age. |
| Soft Cheeses (e.g., Brie) | MK-8, MK-9 | ~56 mcg | Content varies depending on the specific cheese. |
| Egg Yolk (from grass-fed hens) | MK-4 | Up to 192 mcg per yolk | Content is highly dependent on the hen's diet. |
| Chicken Liver | MK-4 | ~12.6 mcg | A solid, if less potent, animal source. |
| Sauerkraut | MK-7 | ~4.8 mcg | Contains small but beneficial levels of K2. |
| Grass-Fed Butter | MK-4 | ~15 mcg | Excellent source of MK-4 from grass-fed dairy. |
Incorporating K2 into Your Diet
For those who find natto's flavor challenging, a balanced diet incorporating a variety of other K2-rich foods is the most practical strategy. The absorption of this fat-soluble vitamin is enhanced when consumed with dietary fat. Thus, combining K2-rich foods with healthy fats can maximize their benefit. A daily rotation of these foods can help ensure a steady intake of different menaquinones. For example, you could add grass-fed butter to your vegetables, include a quality aged cheese on a salad, or enjoy an occasional serving of chicken liver. For many, supplementation remains a reliable option to ensure adequate intake, particularly with the highly bioavailable MK-7 form, but dietary sources should always be prioritized. For those considering supplements, consulting a healthcare professional is advisable, especially if taking blood thinners like warfarin.
Conclusion: Prioritizing K2 Intake
While the search for the single food with the highest K2 content leads to natto, a broader understanding of K2-rich foods is far more useful for overall health. A combination of fermented and animal-based products, especially dairy from grass-fed sources, can provide a variety of menaquinones essential for bone and cardiovascular health. Focusing on integrating these foods into a regular, balanced diet is a sustainable way to reap the benefits of this often-overlooked nutrient. Remember to combine K2 sources with a healthy fat to aid absorption, and consider your dietary preferences and health goals when planning your intake.
